This invention relates to liquid immersion development (LID) reproduction machines, and more particularly to such a machine having a multiple zone image development and conditioning apparatus.
Liquid electrophotographic reproduction machines are well known, and generally each includes an image bearing member or photoreceptor having an image bearing surface on which latent images are formed and developed as single color or multiple color toner images for eventual transfer to a receiver substrate or copy sheet. Each such reproduction machine thus includes a development system or systems that each utilizes a liquid developer material typically having about 2 percent by weight of charged, solid particulate toner material of a particular color, that is dispersed at a desired concentration in a clear liquid carrier.
In the electrophotographic process of a LID machine, the latent images formed on the image bearing surface of the image bearing member or photoreceptor are developed with the charged toner particles, with excess liquid carrier being left behind or removed such that the developed images typically each contain about 12 percent by weight of the toner particles. The developed image or images on the image bearing member are then further conditioned and subsequently electrostatically transferred from the image bearing surface to an intermediate transfer member. Following that, the conditioned image or images are then hot or heat transferred from the intermediate transfer member, at a heated transfer or transfix nip, to an output image receiver substrate or copy sheet.
LID machines, as above, conventionally include a liquid developer material or ink applicator for supplying or applying an even layer of the ink for image development. As pointed out, ink or liquid developer material being supplied by the applicator is about 2% solids (by weight) and developed images are on the order of 10%-15% solids (by weight). Such machines also include a biased metering roll for metering an amount of carrier fluid in the ink as well as for developing images with the metered ink. Fluid metering as such, and image development, are conventionally carried out separately, and typically by using a reverse rolling or moving metering roll. Reverse is used here in the sense that, in a nip formed between the separate metering roll and the image bearing member, the separate metering roll is moving in a direction opposite to that of the image bearing member. Reverse metering rolls have been found to produce images that are subjected to high drag out or smear effects due to high shear forces between the reverse roll and the image being developed.
LID machines typically also include a step of conditioning the initial ink developed image, so as to provide increased image stability, by raising the percent solids content of such image from the 10%-15% solids (by weight), to at least 25% (by weight). Conventionally, such image conditioning is accomplished using a device that is separate from the ink metering and image development devices. Disadvantages of conventional LID machines as such therefore include relatively larger machine architectures, relatively more machine components and hence greater costs, and relatively poorer image quality due to the shear forces.
Conventional practice in LID is then to introduce the developing liquid at point far away from the minimum gap of a development coating nip, develop the image in the nip, meter the developed image on the photoreceptor by hydrodynamic shear created by the counter rotation of a metering roll, and finally blot the image with a low solids image conditioning (LSIC) device, such as a squeegee roll. The function of the low solids image conditioning (LSIC) device is to remove excess liquid from the imaged photoreceptor and to stabilize the image. The removal of this clear liquid increases the solids concentration in the toned image areas typically from 7% to about 20%. In the process of increasing solids concentration, the liquid layer thickness is reduced from 15-20 microns down to 5 microns. Liquid thicknesses of 15-20 microns exiting the development and metering zone are obtained by rigidly maintaining a gap of about 0.002"-0.003" with very tight tolerances. To have proper development, the nip geometry is important. For example, to enable development at high process speeds with highly viscous liquids (of about 2.5 centipoise), the development zone length should be fairly long and the gap with liquid should be fairly large. This can be accomplished conventionally with a large diameter roll such as a 6" roller. However, experimental and modeling studies have shown that the metered image thickness is proportional to the metering gap but not sensitive to the metering roll diameter.
There is therefore a need for a LID reproduction machine having a liquid developer coating device and an image development and conditioning apparatus for removing, from background areas of an image being developed, liquid developer material consisting of liquid carrier and charged solid toner particles, and from image areas only excess carrier liquid, thereby creating a resulting toner image having a toner concentration significantly higher than the first toner concentration of the liquid developer material.